The invention relates generally to a method and apparatus for controlling torque delivery to the rear wheels of a front wheel drive vehicle and more particularly to a method and apparatus for controlling independent engagement of clutches disposed at the rear of a front wheel drive vehicle that asymmetrically provide drive torque to the respective rear wheels.
Extensive effort has been directed to many aspects of vehicle control and performance in vehicles equipped with adaptive four-wheel drive systems. Since the opportunity exists in vehicles equipped with four-wheel drive systems to monitor and control torque application to all four vehicle wheels rather than simply two wheels, as in many vehicles, the opportunity to significantly enhance the performance and performance characteristics of such vehicles also exists.
Many patented systems address and exploit the capabilities of four-wheel drive systems in manners intended to, for example, provide skid control, provide optimum acceleration and deceleration, or provide maximum acceleration and deceleration subject to maintaining vehicle control.
In addition to skid or slip sensing and control, a recent area of patent activity can be characterized as control of vehicle yaw, that is, motion of the vehicle about its Z or center, vertical axis.
For example, U.S. Pat. No. 5,332,059 teaches a four-wheel drive vehicle control system having a steering angle sensor and a clutch disposed across a rear differential. The clutch inhibits differentiation in response to sensed vehicle speed, steering angle and longitudinal and lateral acceleration.
U.S. Pat. No. 5,341,893 discloses a four-wheel drive system for a vehicle such as a tractor wherein a front differential drives left and right front wheels and torque is supplied to the rear wheels through individual clutches.
U.S. Pat. No. 6,076,033 teaches a process for controlling yaw in a motor vehicle through the generation of mutually exclusive braking and driving forces on the left and right wheels of a vehicle.
Another four-wheel drive system appears in U.S. Pat. No. 6,145,614 which discloses a four-wheel drive system having a center differential with a differentiation inhibiting device disposed across the differential and a second differential at the primary axle which also has a differentiation inhibiting clutch disposed there across. The system also includes a turn sensor and means for adjusting the extent of differentiation inhibition depending upon the speed difference between the right and left main drive wheels.
From the foregoing survey of patents directed to motor vehicle yaw control, it is apparent that improvements to the subject art are desirable.